The biggest thing what will help you with Basic is to have fun (I thought boot camp was hilarious and I went to Parris Island!) and remember that millions of other Joes have gone through training and made it!

RandyB is right, you'll have to start at square one if you decide to go Marine later on.

I don't know where you are in your process, but I'd advise that you look at both services and their available MOS's and see what's best for you. Pick one and stick with it - who knows, you may even make it a career!